Mileva, Aleksandra

Preferred name

Mileva, Aleksandra

Official Name

Mileva, Aleksandra

Main Affiliation

saskamileva@yahoo.com

Now showing 1 - 9 of 9

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Applications of Quasigroups in Cryptography and Coding Theory
(Springer, 2023)
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Popovska-Mitrovikj, Aleksandra
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SBIM (Q)-a Multivariate Polynomial Trapdoor Function over the Field of Rational Numbers
(2014)
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. In this paper we define a trapdoor function called SBIM(Q) by using multivariate polynomials over the field of rational numbers Q. The public key consists of 2n multivariate polynomials with 3n variables y1, . . . , yn, z1, . . . , z2n. The yi variables take care for the information content, while the zi variables are for redundant information. Thus, for encryption of a plaintext of n rational numbers, a ciphertext of 2n rational numbers is used. The security is based on the fact that there are infinitely many solutions of a system with 2n polynomial equations of 3n unknowns. The public key is designed by quasigroup transformations obtained from quasigroups presented in matrix form. The quasigroups presented in matrix form allow numerical as well as symbolic computations, and here we exploit that possibility. The private key consists of several 1×n and n×n matrices over Q, and one 2n × 2n matrix.
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Some Generalizations Of Recursive Derivates of k-ary Operations
(2018-08-07)
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We present several results about recursive derivates of kary operations defined on finite set Q. They are generalizations of some binary cases given by Larionova-Cojocaru and Syrbu [7]. Also, we present several experimental results about recursive differentiability of ternary quasigroups of order 4. We also prove that the multiplication group of k-ary quasigroups obtained by recursive differentiability of a given k-ary quasigroup (Q, f) is a subgroup of the multiplication group of the (Q, f).
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MSWordSST – A New Steganalytical Tool for Microsoft Word Documents
(2020-09-24)
Stojanov, Ivan
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Stojanov, Done
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Stojkovich, Natasha
Text steganography is the art of hiding data in the text messages or text documents, so that no one suspects it exists. As opposite, the basic task of steganalysis is to detect which carriers have secret bits encoded in them. In this paper, we present a new software tool for steganalysis of nine different format-based steganographic methods in MS Word documents. First, we describe the detection features that we use, which are extracted from the examined document, and after that, we perform experiments for performance analysis of the tool on the legitimate documents and generated stego documents obtained by four property coding methods.
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Periodic quasigroup string transformations
(2009)
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Given a finite quasigroup (Q,*), a quasigroup string transformations e_l and d_l over the strings of elements from Q are defined as follows. e_l(a_1a_2 ... a_n) = b_1b_2 ... b_n if and only if b_i = b_{i-1}*a_i and d_l(a_1a_2 ... a_n)= b_1b_2 ... b_n if and only if b_i = a_{i-1}*a_i, for each i = 1,2, ... ,n, where l=a_0=b_0 is a fixed element of Q. A quasigroup string e- or d-transformation t is periodical if for some periodic string we have t(a_1a_2 ... a_k a_1a_2 ... a_k ... a_1a_2 ... a_k) = a_1a_2 ... a_k a_1a_2 ... a_k ... a_1a_2 ... a_k. The quasigroup string transformations are used in many fields, like: cryptography for designing different cryptographic tools, coding theory for designing error-detecting and error-correcting codes, etc. The properties of the quasigroup string transformations depend on the used quasigroups, and some quasigroups are suitable for cryptographic designs, while some others are suitable for code designs. We give a characterization of the quasigroups producing periodic string transformations, and for that aim quasigroups with period k are defined. One can use this characterization for choosing suitable quasigroups in some applications.
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On a conditional collision attack on nasha-512
(2009)
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Gligoroski, Danilo
A collision attack on NaSHA-512 was proposed by L. Ji et al. The claimed complexity of the attack is 2192. The proposed attack is realized by using a suitable differential pattern. In this note we show that the correct result that can be inferred from their differential pattern is in fact a conditional one. It can be stated correctly as follows: A collision attack on NaSHA-512 of complexity k = 1, 2, . . . , 2 320 can be performed with an unknown probability of success pk, where 0 ≤ p1 ≤ p2 ≤ p2 320 ≤ 1. Consequently, the attack proposed by L. Ji et al. can be considered only as a direction how a possible collision attack on NaSHA-512 could be realized. The birthday attack remains the best possible attack on NaSHA-512.
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Information Hiding in the DICOM Message Service and Upper Layer Service with Entropy-Based Detection
(MDPI, 2022-01-25)
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Velinov, Aleksandar
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Caviglione, Luca
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Wendzel, Steffen
The DICOM (Digital Imaging and COmmunication in Medicine) standard provides a framework for a diagnostically-accurate representation, processing, transfer, storage and display of medical imaging data. Information hiding in DICOM is currently limited to the application of digital media steganography and watermarking techniques on the media parts of DICOM files, as well as text steganographic techniques for embedding information in metadata of DICOM files. To improve the overall security of the DICOM standard, we investigate its susceptibility to network steganographic techniques. To this aim, we develop several network covert channels that can be created by using a specific transport mechanism – the DICOM Message Service and Upper Layer Service. The bandwidth, undetectability and robustness of the proposed covert channels are evaluated, and potential countermeasures are suggested. Moreover, a detection mechanism leveraging entropy-based metrics is introduced and its performance has been assessed.
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Frequency Distribution of Letters, Bigrams and Trigrams in the Macedonian language
(2012)
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Panov, Stojanche
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Frequency analysis in cryptanalysis is based on the fact that, in any given piece of written text, certain letters and combinations of two or three letters occur with varying frequencies. In this paper we present average frequency distribution of letters, bigrams and trigrams in the Macedonian language. Letter frequency of the most common first letter and last letter in words is also given. Our results are based on approximately 15000 pages of written text from the following subjects: poetry, prose, drama, natural sciences, social sciences, law, different laws, economy, and computer science. Obtained letter frequency sequence is “А О И Е Т Н Р С В Д К Л П М У З Ј Г Б Ч Ш Ц Ж Њ Ф Ќ Х Ѓ Џ Љ Ѕ”, the most common letter pairs are “НА АТ ТА НИ ТЕ РА ОТ СТ ТО КО” and the most common trigrams are “ИТЕ АТА УВА ИЈА АЊЕ СТА ОСТ ВАЊ ПРО ПРЕ”.
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Applications of Quasigroups in Cryptography and Coding Theory
(Springer International Publishing, 2023)
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This survey article discusses some applications of quasigroups in cryptography and coding theory. Here mainly results obtained by the authors of this article are considered and obtained in the last quarter of the century. Not all of their results are presented; emphasis is given to those that were interested for the wider community. Security of the modern world is dependent on the many cryptographic products like block ciphers, stream ciphers, digital signatures and encryption schemes, hash functions, pseudo-random number generators, ... These products are mainly produced by using associative structures (number theory, group and finite field theory, Boolean algebras, etc.) The development of quantum computers questioned security based on associative structures. So, nowadays, the use of quasigroups for building cryptographic products is becoming more important. This short survey presents how quasigroups can be exploited for building suitable cryptographic primitives. For that aim, we define some types of quasigroups that are suitable for that purpose, we give the definitions of several kinds of quasigroup transformations, and we explain the constructions of some types of cryptographic primitives obtained by quasigroup transformations. (We notice that cryptographic properties are not discussed in this survey. The efficiency and security of the crypto products based on quasigroups is an open research problem for cryptographers and cryptanalysts.) The quasigroups are also suitable algebraic structures for building error detecting and error correcting code. We give one type of error detecting code based on quasigroups. Error correcting codes resistant to an intruder attack, so called RCBQ (Random Codes Based on Quasigroups) are given in details, as well as some of their applications in processing images and audio signals.

Mileva, Aleksandra

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